To assure aeronautical conspicuity, any temporary or permanent object, or portion thereof, that exceeds an overall height of 200 feet AGL (above ground level), including all appurtenances, such as lights, rods, antennas, towers, etc., or any object that exceeds any obstruction standard contained in FAR (Federal Aviation Regulations), Part 77, subpart C, should be marked and/or lighted in accordance with described standards. Normal outside or commercial lighting is not sufficient.
Marking warns pilots on a potential collision course with a structure of its presence during daylight hours. This may be accomplished by coloring the structure or indicating its presence by the use of suitable markers, such as flags or spheres.
Lighting is used to warn pilots on a potential collision course with structure during the day or the night. Red obstruction lights are used during the hours of darkness and periods of limited daytime illuminance and/or reduced meteorological visibility. Flashing aviation red beacons and steady burning aviation red lights are normally used during the night. Flashing high intensity white obstruction lights are mostly used during daytime, with automatically selected reduced intensity for twilight and nighttime operations. Flashing medium intensity white obstruction lights, with automatically selected reduced intensity for night operation, are also used. A combination of flashing aviation red beacons and steady burning aviation red lights for nighttime and flashing high or medium intensity white lights may be used for daytime. Dual obstruction lighting systems may not be recommended when an aeronautical study determines that if it is not feasible to operate a high intensity or medium intensity white lighting system at night. Current details regarding marking and lighting systems are contained in FAA Advisory Circular 70/7460-1G. Light systems should conform with the provisions of AC 150/5345-43, "Specifications for Obstructional Lighting Equipment".
There are advantages in using flashing white obstruction lights. First of all, a flashing light attracts attention. Secondly, it may be more visible during certain overcast conditions. From a practical point-of-view, painting tall structures to provide a warning by marking is not only expensive, but also hazardous.
There is also an incentive under current federal regulations to use flashing white obstruction lights. For example, when high intensity flashing white lights are operated during daytime and twilight, other methods of marking may be omitted. Moreover, when flashing medium intensity white obstruction lights are used on structures 500 feet AGL or less in height, other methods of marking and lighting the structure may be omitted; when operated 24 hours a day, other methods of marking and lighting may be omitted. High intensity flashing white lighting systems should have an intensity of: 200,000 candela during the day mode; 20,000 candela during the twilight mode; and 2,000 candela during the night mode. Medium intensity flashing white lighting systems lights should have an effective intensity of no less than 20,000 candela for the day and twilight modes, and approximately 2,000 candela for the night mode.
Because of the advantages of using flashing white obstructions lights, it would be preferable to convert a red obstruction light system to a flashing white obstruction light system. Although, strobe light devices and the methods used for producing a strobe light using the discharge of capacitors are known to exist, they do not, for the most part, use an existing lighting fixture. For example, there is the STROBEGUARD beacon by EG&G and the ELECTROFLASH beacon by Enterprises Inc. which use a new light fixture (See AC 70/7460-1G, Appendix 1, beacon L-866).
Strobe lights are the subject of certain patents (See U.S. Pat. Nos. 4,139,805; 4,185,232; 3,953,763; 4,580,201; and 4,613,797 for some examples). It is believed that the prior art does not disclose or suggest a strobe light system which can be used with an existing incandescent tower light fixture in such a manner as to meet the requirements of the Federal Aviation Administration.
Preferably, if one were to convert or retrofit a red obstruction light system to a flashing white obstruction system, the conversion should use as much of the existing wiring as possible, especially those parts located high on the obstacle or tower structure. Moreover, it would be desirable to use the existing lens and base of the incandescent light fixture. Typically, such light fixtures use an industry or code standard known as a 300 MM code beacon incandescent tower light fixture; such a fixture has a 9.75 inch, 4-hole, metal base which fits on a standard beacon mounting plate on the obstacle or tower structure. 120 V AC, 50/60 hertz, single phase electrical power is supplied to a socket and/or terminal board in the base of the fixture generally from a waterproof junction box mounted near the base of the light fixture. Hingedly connected to the base is a clear glass Fresnel lens. (See AC 70/7460-1G Appendix 1, beacon L-866).